You're doing lots of exercise?
It may be that despite what you might want to weigh you just can't get that low if you're a muscly type of build.
Arnold schwartzenegger was classed as obese on the bmi chart when he was mr universe so don't go by that.
It may be you're toning / building muscle at a similar rate to losing fat so there won't be that big of a difference each week.
Get the tape measure out and the weeks you're slow you'll probably find you've lost inches or built muscle.
Try more greens in general an cut back on the bananas.. ( they don't do me much good )